Patent GB-781534-A (GB)
Title: Improvements in or relating to nitric acid esters of cellulose and process of preparing same
Inventor: BENNETT JAMES LEROY
IPC: C08B17/04
Filed: 1955-09-20
Abstract: <PICT:0781534/IV (a)/1> <PICT:0781534/IV (a)/2> <PICT:0781534/IV (a)/3> Cellulose nitrate is made by reacting cellulose with a nitrating mixture containing about 45-80 per cent of nitric acid, about 10-34 per cent of magnesium nitrate, and about 7-21 per cent of water by weight, the ratio of magnesium nitrate to water being about 1.2-2.2, preferably 1.5-2.0, and the ratio of nitrating mixture to cellulose being preferably at least 20 : 1 by weight. The nitration may be continuous and may conveniently be carried out at 15-70 DEG C. in the apparatus of Figs. 1 and 2 if the cellulose is in the form of cotton linters or shredded cellulose, or in the apparatus of Fig. 3 if in sheet form.  As shown in Figs. 1 and 2, the cellulose is introduced through line 11 into nitrating vessel 13, into which nitrating mixture in predetermined amount is also passed through line 12.  After nitration the suspended nitrocellulose is passed to centrifuge 15, where the bulk of nitrating mixture is centrifuged off and passed through line 16 to storage tank 38.  The nitrocellulose in the centrifuge is then given a displacement wash with 60-75 per cent nitric acid introduced by line 17, the discharge from this wash passing through line 18 to tank 55.  The nitrocellulose is discharged from centrifuge 15 through pipe 19 to centrifuge 21, where it is given a series of washes with nitric acid of decreasing concentration, the final wash preferably being water and the wash liquids being supplied through lines 24, 28, 33, and finally 35, in succession.  The discharge from the first wash is passed through line 25 to tank 55 but the discharges from the succeeding washes, as they take up nitric acid retained by the cellulose and so become more concentrated, are successively passed to the preceding acid storage tank and so become the wash liquor for an earlier stage.  After the final wash the nitrocellulose is passed through pipe 37 to any conventional equipment for after-treatment.  Part of the spent nitrating mixture from storage tank 38 passes through lines 39, 41, 43 to mix tank 44, where it is fortified with concentrated acid fed by line 71 and concentrated magnesium nitrate fed by line 102 and then passes, via storage tank 48 and heater 53, back along line 12 to nitrating vessel 13.  The rest of the spent nitrating mixture which has accumulated in tank 38 passes along lines 39, 54 to the acid concentrator feed tank 55, into which the displacement and first wash have also been passed.  The acid from this tank passes along lines 56, 58 to the stripping zone in the upper portion of nitric acid concentrator 59.  Recovered (72 per cent) magnesium nitrate solution is also simultaneously passed by line 61 to the upper zone, where it acts as the dehydrating agent in the concentration of nitric acid. The concentrated acid is condensed in 63 and part is refluxed by line 65, the remainder being collected in tank 67, whence it is fed by lines 68, 71 to mix tank 44, where it fortifies the spent nitrating mixture as previously described. The still bottoms are taken off by line 72, and part is returned by boiling tubes 74 and line 75 to supply heat for the distillation.  The rest of the still bottoms is passed to the magnesium nitrate recovery still 77.  The bottoms from this still (approximately 72 per cent concentration) are partly recycled (lines 83, 85, 86, 88 and boiling tubes 87), partly passed to the nitric acid concentrator by line 61, and the rest passed to the second magnesium nitrate recovery still 91 by line 89.  As before, the bottoms from this second still are recycled in part by lines 95, 97, 98, 101 and boiling tube 99, but the rest is conveyed by line 102 to mix tank 44 to fortify the spent liquor.  The water from the two magnesium nitrate stills is condensed in condensers 79, 93 and passed to the hot well 82.  Fresh nitric acid to replace that lost in the nitration enters by line 103 to storage tank 104, whence it passes partly to centrifuge 15, where it is employed as the displacement wash, and partly to reactor tank 107, where it is mixed with predetermined amounts of magnesium carbonate, oxide or hydroxide which enter through line 105 and react to form magnesium nitrate solution.  This solution then passes through filter 109 to tank 111, and from there to the first magnesium nitrate still 77 by line 112. Fig. 3 shows another embodiment of the invention in which a roll of sheet cellulose 1 is passed through bath 5 of nitrating mixture, which is continuously being removed from the bath by suction device 13 to be fortified as before.  The sheet is then subjected to a displacement wash in zone A and to further washes in zones B, C, D, E with nitric acid of decreasing concentration, the washings being thereafter used in the preceding washing zone.  After the last zone, the sheet is disintegrated in vessel 49 by roll 53 and the slurry passes out into hold tubs.  The fortification and replenishment of the nitrating mixture is carried out as already described with reference to Fig. 2.  Nitrocellulose made as described above may be stabilized by incorporating 0.2-2 per cent, preferably about 1 per cent, of diphenylamine and also 0.02-1 per cent of an acid having a dissociation constant not greater than 0.02, tartaric, citric, stearic, phosphoric and toluenesulphonic acids being named.